Electric furnace



Oct. 18,1927. 3%

F. A. J. FITZ GERALD I ELECTRIC FURNACE Filed May 26, 1925 2 Sheets-Sheet I I a w'gx/pwbw i a N v ve'n o1 v ygw gia zzsAll ilgflzmld Oct. 18,, 1927.

F. A. J. FlTZ GERALD ELECTRI C FURNACE Filed May 26. 1925 2 Sheets-Sheet 2 W QN M 0 WWW w m a at J m, .M IMW m .e f Fm NMM I I 2 &

Patented Oct. 18, 1921. V

UNITED STATES PATENT oFFIcE.

FRANCIS A. J. FITZ GERALD, OF NIAGARA FALLS, I EW YORK, ASSIGNOR TO HARPER ELECTRIC FURNACE CORPORATION, A CORPORATION OF NEW YORK.

Emerald ruaiucn,

Application filed Kay 26, 1925. Serial Io.'32,879.

This invention relates to electric furnaces of the resistance type which may be used.

for heat treating substances and bodies of different kinds, i and forms in a variety of.

Ways, such as fcuring, baking and glazing ceramic bodies; annealing, tempering, welding and fusing metals; and cremating, firing and burning materials and bodies.

Among the objects of my invention is to provide an improved electric furnace which shall be simple and economical inconstruction, durable in use, and which may be easily and efficiently operated.

In the preferred embodiment of my invention, I provide an electrically heated furnace wherein the resistors are contained within a closed heat chamber that may be 'kept filled with a gas, vaporor fume of such kind or quality as will render the V resistors immune to, or protected from, deterioration such as may be caused by oxygen of the air or gases arising from the material being treated. The material .or articles to be treated are contained in a 25. chamber adjacent to the heat chamber but separated therefromby a septum formed of material which is highly receptive, conductive and emissive of heat but is substantially non-reactive in the presence of atmospheric oxygen at high temperatures. The material forming the septum or division between the heat chamber and the chamber containing the material treated forms one of the important features of my invention. I prefer- 5 ably form the septum of carborundum, and particularly a form of carborundum which I will describe in detail hereafter. In the preferred form of my invention, I also, line the walls of the heat chamber with this 0 material so as to provide a path along which radiant heat received by the walls of the heat chamber may be conducted to the chamber containing the material treated.

Numerous objects and advantages of my 5 invention will appear from the following description, taken in connection with the accompanying drawing,.wherein Fig. 1 is a view, partly in section on the line A of Fig. 2, partly in elevation and 0 partly broken away, of a furnace disclosing one embodiment of my invention.

' Fig. 2 is a section, partly broken away, taken on the line B of Fig. 1.

Fig. 3 isa transverse section on a somewhat enlarged scale taken on the line C of Fig. 1 and showing certain further details of construction.

Fig. 4 .is a diagrammatic view of a referred arrangement and disposal of the rnace resistor element 'or elements. A

Referring to drawing, the heat-producing element 5 is preferably the so-called raphi tized carbon zigzag resistor formed y cut-- ting a series of blind-staggered slots 6 extending transversely of the block or slab. Graphitized carbon is a readily obtainable commercial commodity in regular sections up to 4 x 10 in. of from 4 to 6 ft. in length. For certain purposes it is preferable to machine or saw the sides at an angle as shown at 7 in Fig. 3 so asto give, a greater radiating surface to the lower face 8 of the resistor 5. The resistor 5 is supported by means of carbonaceousterminals, 9, 10 as shown in Figs. 1, 2 and 3 pro'ecting -through the Wall of the furnace. he connection between the terminals and resistor may be formed by a slip jointr' If desired to secure adequate electrlcal connection with the ter-' minals, such joint may be formed to provide a wedge fit, or such connections completed by packing with powdered graphite or carbonaceous ,material, not shown. In this manner, the resistor .is supported between the terminal connections. When a resistor isdesired ofjgreater length than can readilybe produced as a monollth, it is quite feasible to join two or more of-such resistors together, end to end, as by capping their contiguous ends'within the furnace; or, if

desired, central terminal or terminals may be extended through the furnace walls and coupled together as shown in Fig. 4: outside ofythe furnace wall which is indicated by a dotted line 16 in Fig. 4. When arranged 1n this manner the two resistors may be operated in series from asource of current 12, or

if it is desired to operate one of the resistors at a higher temperature than the other the connector block 13 between the adjacent terminals 9 and 10 of the two resistors may be removed and the resistors supplied from separate sources, as indicated at 14 and 15 in Fig. 4:. With such an arrangement, if either resistor becomes inoperative, the other resistor can be run under a current overload, thereby. avoiding the loss of the charge.

The resistor chamber D is bounded by relatively massive roof-slabs, or tiles, 17

side-slabs 18, 19 and floor plates 20, all being supported by anotherv series of carborundum uprights 21 and foot-blocks 22, leaving an interposed gap E connecting with an enlarged runway F, to receive a car, or series of cars, as 23, 24 and 25, mounted on wheels 26, and whose upper plates, or platforms, as 28 Figure 3, are also formed of carborundum. The said floor plates 20, constitute a heat-transferring septum from'the resistor chamber, D, to the underlying conduit chamber H. Paralleling the outer surfaces of the chamber Walls are wall gaps filled with carborundum sand, 29. The outer roof may be suitably formed toreceive pulverized, non-heat-conductive refractory material and the entire furnace may then be fur ther enveloped with material most effective to resist the outward flow of low-temperature heat, as indicated by the broken contour line 30. i

It will now doubtless be apparent that the .path of least resistance for the flow of heat units from the lower surface of the resistor will be, as see arrows a, to andthence, by conduction, through the septum, from whence they proceed, b radiation, as see arrows b, to the car-plat orms and whatever may be mounted thereon. ..Concurrently, however, and particularly from its sides, resistor heat will be imparted, as see arrows 0, to the resistor chamber sidewalls, it being thence -most freely conducted downwardly into the supporting side walls, and foot blocks, escaping by radiation, as see arrows (Z, to the charge and the car platform. Nate urally, a portion of the transferred energy is lost through the car-clearance s aces of the gap E; but the actual sum of t is, relative to the whole, is comparatively nominal and usually negligible.

As the mass of downwardly heat-conducting carborundum in the walls of the resistor chamber may be many times greater than that of the resistor, and as these carborundum walls conduct the heat from the resistor with a comparatively small drop in temperature, and as this greater mass of carborundum serves as a heat reservoir, therefore fluctuations of temperature directly in and at the resistor itself are diminished. The transfer of heat units is rapid and eflicient notwithstanding the interposed septum, in that the septum is a good conductor of heat and suflicient difference in temerature between the resistor and the charge is permissible to obtain such transfer.

As a lining for the heat chamber and the chamber containing the material to be treated, I employ carborundum, preferably a form of carborundum which I prepare in the following manner. The carborundum in the form of grains or powder, as supplied commercially, is mixed with a temporary binder such as flour paste or the like, and is then molded into the desired forms. The articles thus formed are then heated in an electric furnace to the temperature at which carborundum is formed, with the result that recrystallization occurs'rand a dense,'monolithic mass is obtained. The blocks, slabs or tiles so formed are then placed in the furnace structure in position to form the linings of the chambers and the septum between the chambers and the furnace may then be heated in the usual manner so as to cause further recrystallization o f the carborundum, thus causing adjacent blocks to coalesce, and the septum and chambers are automatically formed devoid of joints. I have indicated the union of the joints by coalescence by wavy lines '31 and 32 in Fig. 3.

a At the high temperature at which the furnace operates, oxygen must be excluded from the chamber containing the resistor, or such. chamber must contain a gaseous medium which will itself react with and wholly convert any oxygen which might otherwise reach the resistor and its juncture with the terminals. The inert gas may be introduced into the resistor chamber by means of a refractory tube 33, Fig. 3, and held under a. head or pressure above that of atmosphere. In certain cases it is feasible to employ an enveloping atmosphere of volatilized zinc, that is, zinc gas or zinc fume. The supply of this material can readily be -maintained by an occasional introduction into the chamber D of molten zinc" In addition to its functioning as an inert gas, zinc gas funcverted by any oxygen presentto zinc oxide,

which eventuallyfills all crevices and prevents escape of the metal. Due to this selfsealing property, a nominal renewal'only of the zinc is required to maintain a suflicient quantity in the heat chamber, such renewal being merely such as' to supply that lost by ventage-escape to avoid an excessive developmentof pressure within the chamber. A further advantage of the use of zinc gas is that it forms an effective heat-convective agent.

Lower tubes 34, Figures 1 and 3, leading to the conduit chamber, may serve a. dual purposeyto permit the escape, or the withdrawal by suction, of air, gases and/or vapors; also to introduce gases and/or vapors,

as for the purpose of producing reducing atmospheres. 1

A plurality of cars, as 23, 24, 25 of Figure 1, each abutting upon another, may be continuously impelled through the furnace conduit at such a rate of motion that, to illustrate, when car 23 will have reached the position occupied by car 25, which is the hot zone of the conduit, the charge conveyed by that car will then be adequately heat-treated; If desired, as in the fusion of non-ferrous metals, annealing iron, or heating steel for hardening and tempering, the terminal ends of the conduit chamber may be enclosed and battened tightly, as at Z, Figure 1. Again,

- readilybe switched at the terminals, circulating through'the chamber conduits with but a nominal heat loss from the cars themselves. V v

I find that the life of resistor or resistors, when operated according to the conditions above set forth, is practically interminable. Nevertheless, should a fracture occur, as from accident or a very slow but progressive oxidation suflicient to eventually cause it to sag and pull apart, it will be perceived, by reference to Figures 1 and 3, that the upper or roof portion of the furnace can readily be broken away, permitting a substitution of resistors even when theinternal chambertemperature is quite-high.

Temperatures in. this furnace can be readily controlled, for indefinite time periods, within plus and minus tolerances of, say, 5 to 10 (1.; but this condition is largely dependent upon pyrometry.

In certain cases, various modifications of the structure and method of operation above described may be made. Thus, in certain cases a carbon or graphitized carbon resistor, even when of the zigzag form, will function satisfactorily if the space within its containing chamber isfilled withcarborundum, or.

with granular carbon or pulverized graphite. Agaim the slab formed of angular cross section of zigzag resistor need not necessarily be adhered to in that it may be cylindrical in transverse section, being encased in a carborundum tube or otherwise formed.

It has been found that the graphite resistor can be greatly improved in its physical.

properties by undergoing heat treating process. This can be carried out by passing current of electricity through the resistor while it is protected/from oxidation so as to heat it to a temperature atleast as high or considerably higher than that at which it will be used in actual practice. When this is done it is found that the resistor is much. tougher and more resilient than it was originally and consequently far less likely to be broken by sudden changes in temperature or by external mechanical forces which would tend to break it. i J

I claim:

1. In an electric furnace, a heat chamber Y having a lining comprising coalescing blocks of carborundum.

2. In an electric furnace, a chamber, a resistor in said chamber, a chamber adjacent to said first-named chamber and adapted to contain material to be heated, and a selfsustaining carborundum partition separat- .ing. said chambers.

3. An electric furnace formed with an interior I space, a self-sustaining septum of carborundum dividing said spaceinto upper and lower chambers, a resistor in the upper of said chambers and the lower of said chambers being adapted to contain material to be heated. p

4. An electric furnace having walls formed of heat-insulating material with an interior lining of carborundum and formed to provide a space within said furnace, a

septum of carborundum dividing said space into'a heat chamber and a chamber adapted to contain material tobe heated.

5. An electric furnace having walls formed of heat-insulating material with an interior lining of carborundum and formed to provide a space within said furnace, a

septum of carborundum dividing said space into aheatchamber and achamber adapted to contain material'to be heated, said lining and septum comprising coalescing blocks of carborundum. p

' 6. An electric furnace having walls formed of heat-insulating material with an in said heat chamber and electric terminals extending through said walls for forminvelectrical connections wlth said resistor and supporting said resistor between said termiloo nals J 7. An electric, furnace having walls formed of heat-insulating material with an interior lining of carborundum and formed to-provide a space within said furnace, a

septum of carborundum dividin said space into a heat chamber and a cham er adapted to contain material to be heated, said lining and septum comprlsing blocks of carborundum coalescing at their junctures to form a monolithic structure, a resistor in said heat chamber and electric. terminals extending through said walls for forming electrical connections with said resistor and for sup-' porting said resistor between said terminals.

8. An electric furnace having walls formed of heat-insulating material with an interior lining of carborundum and formed to provide a space within said furnace, a septum of carborundum dividing said space I into a heat chamber and a chamber adapted,

to contain-material to be heated, and a graphite resistor insaid heat chamber supported free of the walls thereof.

9. An electric furnace having walls formed of. heat-insulating material with an inte tumof carborundum dividing said space into a heat chamber and a chamber adapted to contain material to be heated, said lining;

and septum comprising coalescing blocks of common side and separating walls formed of carborundum, and agra' bite resistor in said heat integrated carborundum. heat chamber supporte free of the walls 12. The method of forming a lining for thereof. n the walls of a. furnace which consists in 10. An electric furnace havinga resistor molding blocks of carborunduxn, firing said chamber and a heat-treatin chamber, comblocks to a, high temperature, building the mon side and separating wa ls ofsaid chamlining of said blocks and subjecting said bers comprising form-maintaining material lining to a temperature suflicient to coalesce heat sealed. said blocks together at their junctures.

l0 11. In an electric furnace, a resistor chamher and a heat-treating chamber having RANCIS ALJ. FITZ GERALD. 

